Throughout this section comparisons with amplitude modulation (AM) will be made. It is recommended that if you are not familiar with AM, you should read that section first.

Armstrong was the almost single handed pioneer of FM broadcasting as well as the inventor of some of the most important aspects of the modern day receiver.

Few people have so revolutionised the field in which they work, fewer still have done it multiple times. That is why Armstrong deserves a page to himself. To read more about this remarkable man, click the link below.



Edwin Harold Armstrong

Frequency modulation is the dominant kind in commercial broadcasting, with four BBC stations and an independent broadcasting nationally, and a myriad of independent and BBC local stations specific to their areas. Despite the advent of digital broadcasting, FM is still the majority choice of listeners and a recent proposal by the last Labour government  in the UK to shut down the FM  bands (along with what remains on AM)  and go all-digital was greeted with widespread protest.


General Theoretical Concerns in FM


As was stated in the last section on AM, all radio communications are made using an electro-magnetic wave that is sinusoidal in nature. We saw that the mathematical value was:









and furthermore that changing anything on the right hand side of the equals sign changes the value on the left. If we now keep Vmax constant, it is possible to change either the phase or the angular frequency.  Either of these methods can be said to be a form of angle modulation, and in frequency modulation we do the latter.  It produces  a waveform such as the one below:


General Theory II

fig 1: Modulated FM wave

Radio Principles